This page has a couple basic interactive tests of the default $.geo.proj object.
Enter a lon/lat in the top inputs (remember, longitude is first here and throughout jQuery Geo but usually spoken second) & click fromGeodetic to convert it to web mercator and store the new values in the bottom two inputs. Click toGeodetic to reverse.
Enter a search term in the input and click search. If successful, geodetic & web mercator coordinates are written to the inputs above. This example uses MapQuest's OSM API: http://open.mapquestapi.com/nominatim.
Status result for any test.